Cathode



Feb. 25, 1947. J. 5 E5 3 2,416,566

- CATHODE Filed Aug. 1, 1942 Jo Fig. I. 3 l0 48 48 l2 I850 l9 67 4-2 so jfj as as Pi .2. 4o 9 M Inventor: James E. Be 25,

His Attorney Patented Feb. 25, 1947 I 2,418,566 camons James E. Beggs, Scotia, N. Y, assignor to General Electric Company, a corporation of New York Application August 1, 1942', Serial No. 453,152;

This is a continuation-in-part of my copending applications Serial No. 449,391 filed July 2,

1942, now Patent No. 2,411,184, and Serial No. 436,633, flied March 28, 1942, both assigned to the General Electric company. 1

The present invention relates cathode.

In high frequency discharge tubes of the type described in theabove-mentioned application it is found expedient to employ a cathode havin an emissive part of disk-like or equivalent form and to provide a supporting structure for such part which is adapted to conduct current symmetrically to the part. This construction has numerous advantages when employed in an ultra high frequency system, but involves certain difficulties with reference to the provision of means for maintaining the emissive part at a suitable emitting temperature. In particular, it proves dimto an improved cult to produce an arrangement which is capable of supplying heat eflectively to the emissive part without concurrently permitting excessive heat loss to and through the supporting-structure.

It is an object of the present invention to provide a cathode which is capable of eflicient operation in a situation such as that specified in the foregoing.

In a typical embodiment, the invention makes use of a hollow structure which serves both as a support for an emissive cathode'p'art and as an enclosure for a heater for such part. Effective heat transfer to the emissive part is provided by means of a thermally conductive body which surrounds the heater and connects directly with the said part while excessive heat loss to the supporting structure is prevented by the fact that the conductive body referred to is interposed between such structure-and the heat source. .Accordingly, the heat flow is directed along lines most conducive to efflcient operation.

The features of the invention desired to be protected herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the drawing in which Fig. 1 is a sectional view of a discharge tube suitably embodying the invention and Fig. 2 is an enlarged sectional view of the cathode of Fig. 1.

Referring particularly to Fig. 1, the discharge tube there illustrated includes a series of three circular metal members It, H and I2 which are arranged in spaced relation and which are mutually separated by glass cylinders l3 and Hi I Olaims. (CL 250-275) sealed between them. Both the metal members III to l2 and the cylinders l3 and M are of progressively decreasing diameter from one end of the tube to the other so that the tube as a whole has a step-wise configuration.

, discharge enclosure. .The glass cylinder I4 is isealed at one end to the upper surface of the planar wall part i8 and at its other extremity to the lower surface of the metal member ll. Similarliithe cylinder I3 is sealed to the upper surface of the member I I and to the lower surface oi. the member ID. In order to facilitate the production of glass-to-metal joints of the kind specified it is expedient to form the part l2 and the disks l0 and H of iron and to use for the cylinders I3 and I4 9. glass which is capable of being sealed to iron, such glasses beingdescribedfor example, in Hull and Navias Patent 2,272,747, granted February 10, 1942. To make the sealing process easier the various metallic parts in question are preferably coated with co per. which has the further effect of increasing the surface conductivity of these members with respect to high frequency currents. It has been found helpful in some cases to silver or gold plate the internal and external surfaces of the parts "I, H and It to assure that these surfaces shall be perfectly clean and resistant to corrosion.

The disk In is provided with a central opening 24 through which extends an anode in the form of a solid cylinder 25. This anode is provided at its upper extremity with a cylindrical terminal 26 which is of lar er diameter than the hole 24. A fused metal joint produced between the terminal 2B and the disk i 0 as indicated at 28 renders this end of the tube vacuum-tight. Below the anode there is provided a mesh grid 30 which extends across a central opening 3| provided in the disk II. The grid is peripherally welded to the disk and has its central portion lying in a. plane which is below the plane of the disk, this construction being preferably produced by deforming the grid in situ as described in my aforesaid Patent No. 2,411,184.

Below the grid and in cooperative relation with both the grid and anode there is provided a cathode having an active or emissive part consisting of a metal (e. g., nickel or molybdenum) disk 40. This disk is preferably coated on its upper surface with an activating coating such as a thin layer of barium and strontium carbonates and is The member It includes a planar portion IB acracec shown in Fig. 2 of the drawing.

The supporting structure for the cathode is of hollow cylindrical configuration and includes a flanged part 42 which extends upwardly through the central opening in the metallic part l2 so as to provide a base for the structure. From this base the emissive disk 40 is supported by means of a cylindrical member 43, which, for reasons that will shortly appear, is preferably constituted of metal foil. The cylindrical member 43 is turned inwardly at its upper extremity as indicated at 44 and the in-turned portion is clamped between the disk 40 and a flange 48 formed at the upper end of a depending metal sleeve 48. Parts 40, 44 and 4B are joined by welding, and in the finished form of the device the flange 46 is in good thermal contact with the disk 40, the spacing indicated in the drawing being substantially eliminated by the welding procedure. The cylinder 43 is of such dimensions that it may be slid over the surfaces of the part 42 in order to facilitate assembly of these elements. After the elements are assembled in the desired relationship, they may be welded to provide a rigid construction.

Within the cathode structure and, more specifically, within the depending sleeve 48, there is provided a filamentary heater 50 which suitably consists of a double helix of tungsten or molybdenum coated with an insulating material such as alumina in order to prevent short-circuiting of adjacent turns of the filament. The lower ends of the filament are supported from relatively rigid lead-in conductors 52 through which heating current may be supplied. As a result of the fact that the filament 50 is enclosed by the sleeve 48, radiation of heat from the filament to the supporting structure 42 is minimized and in this way the heat loss of the cathode heating system is reduced to a low value. At the same time the sleeve 48, which is preferably constituted of a metal of high thermal conductivity, such as copper or nickel, affords an effective path for heat flow to the emissive disk 40.

Loss of heat from the part 40 to the supporting structure is minimized by forming the cylinder 43 of a foil which has a thickness on the order of a few tenths of 2. mil so that it provides a high impedance heat path from the disk 40 to the part 42. In order to assure maximum heat-throttling efiect the cylinder 43 may suitably consist of a metal of low thermal conductivity such as an iron-nickel-cobalt alloy (fernico). I wish to point out, however, that the use of a metal foil in the manner indicated is in a broad sense the prior invention of Ralph J. Bondley, being claimed by him in his application Serial No. 448.541 filed June 26, 1942, now Patent No. 2,367,332 and assigned to the General Electric Company. It is not intended to be claimed herein except insofar as it forms a component element of the improved cathode construction described in the foregoing.

In order to mount the cathode structure within the discharge enclosure, the flange 42 of the part 42 is secured by welding or otherwise to relatively rigid lead-in conductors 55 which tend to press the flange 42' against the under surface of the envelope part l8, direct contact between these parts being prevented by the interposition of an insulating (e. g. mica) disk 51. This disk permits the cathode structure to be at a different D. C. potential from that of the envelope part l2, while nevertheless being efiectively directly connected to it as far as high frequency currents are cond cerned by the capacitive coupling through the disk. As a consequence the part i2 is adapted to serve as a high frequency terminal for the oathode structure.

As is fully explained in my aforementioned Patent No. 2,411,184, tubes intended for use in an ultra high frequency system require that low inductance terminal connections be provided to the various electrode elements. This requirement is fully met by the cathode structure described in the foregoing disclosure in that a symmetrical current path of extremely low inductance is provided to the emissive disk 40 through the member i2, the cylindrical base part 42 and the foil cylinder 43.

Unidirectional current may be supplied to the cathode by means of the conductors 55, these conductors and the filament lead-in conductors 52 being sealed through a metallic closure member 60 which is secured by a vacuum-tight soldered joint 45 to the lower edge of the circular rim 20. Individual glass-to-metal seals 62 corresponding in number to the lead-in conductors, serve to maintain the conductors in insulatingly spaced relation with respect to the part 60. The externally extending extremities of the lead-in conductors are soldered into tubular contact prongs 63, and these, in turn, are supported in an insulating adaptor which is suitably secured in engagement with the closure member 60. A centering post 65 which depends from the adaptor 84 serves to facilitate the orientation of the tube in a cooperating socket.

While the invention has been described by reference to a particular embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without departing from the invention. I. therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A cathode structure comprising, an emissive part, a hollow support therefor, an electrical connection between said support and said emissive part having high impedance to heat flow and serving mechanically to support said emissive part from said hollow support, a heater within said support, and a thermally conductive body around said heater and interposed between said heater and support and having good thermal connection to said emissive part, and serving both to conduct heat to said part and to prevent radiation of heat to said support whereby heat loss through said support is reduced.

2. A cathode comprising an emissive part. a hollow structure having said part as an end wall thereof, a heater within said structure and a tubular metallic element surrounding the heater and interposed between the heater and said structure and extending in spaced relation with respect to said structure, said element having a good thermal connection at one extremity with said emissive wall part and serving conjointly to conduct heat to said part and to minimize radiation of heat to said structure.

3. A cathode comprising a metallic disk of thermionically emissive character, a hollow structure supporting the disk and having the disk as an end wall of thestructure, a heater within the said hollow structure, a metallic sleeve surrounding said heater and interposed between the heater and the said hollow structure and extending in spaced relation with respect to said hollow structure. and a flange on said sleeve at one end thereof providing a thermally conductive connection between the sleeve and the said disk.

4. A cathode comprising an emissive part, a hollow supporting structure for said emissive part, said structure comprising a base portion and a further portion of low thermal conductivity and high electrical conductivity located between said base portion and said emissive part for minand conducting current between said emissive part and said base portion, a heater within said structure, and an element of high thermal conductivity surrounding said heater and interposed between the heater and said structure, said element being connected to said emissive part and providing an efiective heat transfer path from said heater to said part.

5. A cathode structure comprising, a pair of I imizing heat flow from-the latter to the former concentric cylinders, an emissive part. the outer of said cylinders having an electrically conductive member attached to one end thereof and supporting said emissive part from said cylinder, said member having high impedance to heat flow from said emissive part to said outer cylinder, and a heater for said emissive part within said innercylinder, said inner cylinder being conductively connected to said emissive part and supported therefrom.

6. A cathode structure comprising, a pair of concentric cylinders, an emissive part, a member of conductive foil about the outer of said cylinders extending beyond the end thereof and supporting beyond said end said emissive part,

said foil forming an electrical connection hav- 8 ing high impedance to heat flow between said cylinder and said emissive part, and a heater within the inner of said cylinders, said inner cylinder forming a path of high thermal conductivity to said emissive part.

'I. An electron discharge device comprising an envelope, a cathode structure comprising two concentric cylinders of diameter small relative to said envelope located near the center thereof, an emissive part supported from the end of the outer of said cylinders through a connection of good electrical conductivity and low heat conductance. said inner cylinder being thermally connected to said emissive part, a heater within said inner cylinder whereby said inner cylinder conducts heat to said emissive part and flow of said heat to said outer cylinder is prevented by said connection of low heat conductance, and said outer cylinder being flared away from said inner cylinder at distances more removed from said emissive part to reduce heat radiated from said inner cylinder to said outer cylinder.

7 JAMES E. BEGGS.

' REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS De Boer May 20, 1941 

